Hydrometallurgical purification of metallurgical grade silicon

The effects of the particle size of ground metallurgical grade silicon （MG-Si）, the sort of acids, and the type of stirring on the purified efficiency of MG-Si were investigated. It was found that a particle size less than 0.1 mm was most effective for acid leaching; the extraction yield of impurities was increased by 9% with HF leaching compared with HCl leaching and HNO3 leaching, and increased by 7% with ultrasonic stirring compared with mechanical stirring. The principle of hydrometallurgical purification of metallurgical grade silicon under ultrasonic fields was also discussed.

Kinetics of iron removal from metallurgical grade silicon with pressure leaching

In this paper, the kinetics of pressure leaching for purification of metallurgical grade silicon with hydrochloric acid was investigated. The effects of particle size, temperature, total pressure, and concentration of hydrochloric acid on the kinetics and mechanism of iron removal were studied. It was found that the reaction kinetic model followed the shrinking core model, and the apparent activation energy of the leaching reaction was 46.908 kJ/mol. And the apparent reaction order of iron removal with pressure leaching was 0.899. The kinetic equation was obtained and the mathematical model of iron removal from metallurgical grade silicon （MG-Si） was given as follows：The values calculated from the equation were consistent with the experimental results.

Boron removal from metallurgical grade silicon by slag refining based on GA-BP neural network

In order to investigate the boron removal effect in slag refining process,intermediate frequency furnace was used to purify boron in SiO2-CaO-Na3 AlF6-CaSiO3 slag system at 1,550℃,and back propagation(BP)neural network was used to model the relationship between slag compositions and boron content in SiO2-CaO-Na3 AlF6-CaSiO3 slag system.The BP neural network predicted error is below 2.38%.The prediction results show that the slag composition has a significant influence on boron removal.Increasing the basicity of slag by adding CaO or Na3 AlF6 to CaSiO3-based slag could contribute to the boron removal,and the addition of Na3 AlF6 has a better removal effect in comparison with the addition of CaO.The oxidizing characteristic of CaSiO3 results in the ineffective removal with the addition of SiO2.The increase of oxygen potential(pO2)in the CaO-Na3 AlF6-CaSiO3 slag system by varying the SiO2 proportion can also contribute to the boron removal in silicon ingot.The best slag composition to remove boron was predicted by BP neural network using genetic algorithm(GA).The predicted results show that the mass fraction of boron in silicon reduces from 14.0000×10-6 to0.4366×10-6 after slag melting using 23.12%SiO2-10.44%CaO-16.83%Na3 AlF6-49.61%CaSiO3 slag system,close to the experimental boron content in silicon which is below 0.5×10-6.

Optimization of the acid leaching process by using an ultrasonic field for metallurgical grade silicon

In the experiment, acid leaching under an ultrasonic field （20 kHz, 80 W） was used to remove AI, Fe, and Ti impurities in metallurgical grade silicon （MG-Si）. The effects of the acid leaching process parameters, including the particle size of silicon, the acid type （HC1, HNO3, HF,） and the leaching time on the purification of MG-Si were investigated. The results show that HC1 leaching, an initial size of 0.1 mm for the silicon particles, and 8 h of leaching time are the optimum parameters to purify MG-Si. The acid leaching process under an ultrasonic field is more effective than the acid leaching under magnetic stirring, the mechanism of which is preliminarily discussed.

Removal of impurities from metallurgical grade silicon by electron beam melting

Solar cells are currently fabricated from a variety of silicon-based materials.Now the major silicon material for solar cells is the scrap of electronic grade silicon（EG-Si）.But in the current market it is difficult to secure a steady supply of this material.Therefore,alternative production processes are needed to increase the feedstock.In this paper,EBM is used to purify silicon.MG-Si particles after leaching with an initial purity of 99.88%in mass as starting materials were used.The final purity of the silicon disk obtained after EBM was above 99.995%in mass.This result demonstrates that EBM can effectively remove impurities from silicon.This paper mainly studies the impurity distribution in the silicon disk after EBM.

Boron Removal From Metallurgical Grade Silicon by Molten Slag Refining in Induction Furnace

The impurities Al,Ca,Ti,B,P etc in metallurgical grade silicon(MG-Si)can be effectively removed by refining using molten slag based CaO-SiO_2,and it is especially effective for boron removal.The experiments of boron removal were studied using CaO-SiO_2 binary slag in induction furnace.The results showed that the distribution coefficient of boron(L_B)between slag and silicon increased with more proportion of CaO/SiO_2(mass%).It was advantaged to boron removal for higher basicity of slag,so the boron in MG-Si was reduced from 18ppmw to 1.4ppmw with the addition of Li_2O and K_2O to CaO-SiO_2 slag.The proportion of SiO_2 in slag affected the oxidizing capacity of slag,which reduced the efficiency of boron removal.